1. Field of the Invention
The present invention relates to numerical controllers and, in particular, to a numerical controller having the function of avoiding interference by assigning priorities to control point commands when performing positioning of a plurality of control points and adjusting movement start timing of a command of lower priority.
2. Description of the Related Art
In the past, if there is a possibility of interference, positioning commands for a plurality of control points have been described in different blocks, not one block, and then executed (Japanese Patent Application Laid-Open No. 2006-075916, for example).
For example, as depicted in FIGS. 8A and 8B, when a loader 2 and a door 3 are controlled by an L axis and an A axis, respectively, in a machine tool 1, commands for the L axis and the A axis are described in different blocks since interference occurs if commands for a retracting operation of the loader 2 and a closing operation of the door 3 are described in one block.
As in the prior art technique, in the method in which control point commands are described in different blocks, objects to be controlled do not interfere with each other because a control operation of a next block is not started until a control operation by a previous block is finished. However, since the next block cannot be started until the operation of the block in which an earlier command is described is completed, the time after the operation of the earlier command proceeds and the state enters a state in which no interference occurs becomes useless waiting time.
The useless waiting time in the prior art technique will be described in detail by using FIGS. 9A to 9E.
FIGS. 9A to 9E are diagrams depicting the flow of operation control by which work is placed by a loader, the loader is retracted, and then a machining operation is started after a door is closed. In the machine tool 1 depicted in the drawings, it is assumed that positioning control of the loader 2 is performed by the L axis and opening and closing control of the door 3 is performed by the A axis and the loader 2 and the door 3 are controlled in accordance with a machining program depicted in FIG. 9A.
When the loader 2 and the door 3 are controlled in accordance with the machining program of FIG. 9A, as depicted in FIGS. 9B to 9E, the door 3 starts to be closed when the loader 2 retracts after finishing placement of the work 4 and machining of the work 4 is started by a tool 5 when the door 3 is completely closed. In the prior art technique, the loader 2 retracts in an N10 block of a program O0001, but execution of an N20 block is not started until the loader 2 completely retracts. If the loader 2 operates slowly, there will be useless waiting time before the start of the closing operation of the door 3.
As an existing function similar to the present invention, there is a “waiting function by specifying start point”. However, this function is a function that allows one path in a multi-path system to coordinate with the other path and cannot be used for coordination in one path. Moreover, coordinate values based on which coordination is performed have to be specified in a machining program, but it is not easy to obtain accurately, based on the movement distance and the movement speed, coordinate values by which interference can be avoided.